/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE
 * file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file
 * to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
 * License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package com.blade.web.multipart;

import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;

/**
 * <p>
 * Low level API for processing file uploads.
 *
 * <p>
 * This class can be used to process data streams conforming to MIME 'multipart' format as defined in <a
 * href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>. Arbitrarily large amounts of data in the stream can be
 * processed under constant memory usage.
 *
 * <p>
 * The format of the stream is defined in the following way:<br>
 *
 * <code>
 *   multipart-body := preamble 1*encapsulation close-delimiter epilogue<br>
 *   encapsulation := delimiter body CRLF<br>
 *   delimiter := "--" boundary CRLF<br>
 *   close-delimiter := "--" boudary "--"<br>
 *   preamble := &lt;ignore&gt;<br>
 *   epilogue := &lt;ignore&gt;<br>
 *   body := header-part CRLF body-part<br>
 *   header-part := 1*header CRLF<br>
 *   header := header-name ":" header-value<br>
 *   header-name := &lt;printable ascii characters except ":"&gt;<br>
 *   header-value := &lt;any ascii characters except CR &amp; LF&gt;<br>
 *   body-data := &lt;arbitrary data&gt;<br>
 * </code>
 *
 * <p>
 * Note that body-data can contain another mulipart entity. There is limited support for single pass processing of such
 * nested streams. The nested stream is <strong>required</strong> to have a boundary token of the same length as the
 * parent stream (see {@link #setBoundary(byte[])}).
 *
 * <p>
 * Here is an example of usage of this class.<br>
 *
 * <pre>
 * try {
 * 	MultipartStream multipartStream = new MultipartStream(input, boundary);
 * 	boolean nextPart = multipartStream.skipPreamble();
 * 	OutputStream output;
 * 	while (nextPart) {
 * 		String header = multipartStream.readHeaders();
 * 		// process headers
 * 		// create some output stream
 * 		multipartStream.readBodyData(output);
 * 		nextPart = multipartStream.readBoundary();
 * 	}
 * } catch (MultipartStream.MalformedStreamException e) {
 * 	// the stream failed to follow required syntax
 * } catch (IOException e) {
 * 	// a read or write error occurred
 * }
 * </pre>
 *
 * @author <a href="mailto:Rafal.Krzewski@e-point.pl">Rafal Krzewski</a>
 * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
 * @author Sean C. Sullivan
 *
 * @version $Id: MultipartStream.java 735374 2009-01-18 02:18:45Z jochen $
 */
public class MultipartReader {

	/**
	 * The Carriage Return ASCII character value.
	 */
	public static final byte CR = 0x0D;

	/**
	 * The Line Feed ASCII character value.
	 */
	public static final byte LF = 0x0A;

	/**
	 * The dash (-) ASCII character value.
	 */
	public static final byte DASH = 0x2D;

	/**
	 * The maximum length of <code>header-part</code> that will be processed (10 kilobytes = 10240 bytes.).
	 */
	public static final int HEADER_PART_SIZE_MAX = 10240;

	/**
	 * The default length of the buffer used for processing a request.
	 */
	protected static final int DEFAULT_BUFSIZE = 4096;

	/**
	 * A byte sequence that marks the end of <code>header-part</code> (<code>CRLFCRLF</code>).
	 */
	protected static final byte[] HEADER_SEPARATOR = { CR, LF, CR, LF };

	/**
	 * A byte sequence that that follows a delimiter that will be followed by an encapsulation (<code>CRLF</code>).
	 */
	protected static final byte[] FIELD_SEPARATOR = { CR, LF };

	/**
	 * A byte sequence that that follows a delimiter of the last encapsulation in the stream (<code>--</code>).
	 */
	protected static final byte[] STREAM_TERMINATOR = { DASH, DASH };

	/**
	 * A byte sequence that precedes a boundary (<code>CRLF--</code>).
	 */
	protected static final byte[] BOUNDARY_PREFIX = { CR, LF, DASH, DASH };

	/**
	 * The input stream from which data is read.
	 */
	private final InputStream input;

	/**
	 * The length of the boundary token plus the leading <code>CRLF--</code>.
	 */
	private int boundaryLength;

	/**
	 * The amount of data, in bytes, that must be kept in the buffer in order to detect delimiters reliably.
	 */
	private int keepRegion;

	/**
	 * The byte sequence that partitions the stream.
	 */
	private byte[] boundary;

	/**
	 * The length of the buffer used for processing the request.
	 */
	private final int bufSize;

	/**
	 * The buffer used for processing the request.
	 */
	private final byte[] buffer;

	/**
	 * The index of first valid character in the buffer.<br>
	 * 0 <= head < bufSize
	 */
	private int head;

	/**
	 * The index of last valid characer in the buffer + 1.<br>
	 * 0 <= tail <= bufSize
	 */
	private int tail;

	/**
	 * The content encoding to use when reading headers.
	 */
	private String headerEncoding;

	/**
	 * <p>
	 * Constructs a <code>MultipartStream</code> with a custom size buffer.
	 *
	 * <p>
	 * Note that the buffer must be at least big enough to contain the boundary string, plus 4 characters for CR/LF and
	 * double dash, plus at least one byte of data. Too small a buffer size setting will degrade performance.
	 *
	 * @param input The <code>InputStream</code> to serve as a data source.
	 * @param boundary The token used for dividing the stream into <code>encapsulations</code>.
	 * @param bufSize The size of the buffer to be used, in bytes.
	 *
	 */
	public MultipartReader(InputStream input, byte[] boundary, int bufSize) {
		this.input = input;
		this.bufSize = bufSize;
		this.buffer = new byte[bufSize];

		// prepend CR/LF to the boundary to chop trailing CR/LF from body-data tokens.
		this.boundary = new byte[boundary.length + BOUNDARY_PREFIX.length];
		this.boundaryLength = boundary.length + BOUNDARY_PREFIX.length;
		this.keepRegion = this.boundary.length;
		System.arraycopy(BOUNDARY_PREFIX, 0, this.boundary, 0, BOUNDARY_PREFIX.length);
		System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);

		head = 0;
		tail = 0;
	}

	/**
	 * Constructs a <code>MultipartStream</code> with a default size buffer.
	 *
	 * @param input The <code>InputStream</code> to serve as a data source.
	 * @param boundary The token used for dividing the stream into <code>encapsulations</code>.
	 */
	public MultipartReader(InputStream input, byte[] boundary) {
		this(input, boundary, DEFAULT_BUFSIZE);
	}

	/**
	 * Retrieves the character encoding used when reading the headers of an individual part. When not specified, or
	 * <code>null</code>, the platform default encoding is used.
	 *
	 * @return The encoding used to read part headers.
	 */
	public String getHeaderEncoding() {
		return headerEncoding;
	}

	/**
	 * Specifies the character encoding to be used when reading the headers of individual parts. When not specified, or
	 * <code>null</code>, the platform default encoding is used.
	 *
	 * @param encoding The encoding used to read part headers.
	 */
	public void setHeaderEncoding(String encoding) {
		headerEncoding = encoding;
	}

	/**
	 * Reads a byte from the <code>buffer</code>, and refills it as necessary.
	 *
	 * @return The next byte from the input stream.
	 * @throws IOException if there is no more data available.
	 */
	public byte readByte() throws IOException {

		// buffer depleted ?
		if (head == tail) {
			head = 0;
			// Refill.
			tail = input.read(buffer, head, bufSize);
			if (tail == -1) {
				// no more data available.
				throw new IOException("No more data is available");
			}
		}

		return buffer[head++];
	}

	/**
	 * Skips a <code>boundary</code> token, and checks whether more <code>encapsulations</code> are contained in the
	 * stream.
	 *
	 * @return <code>true</code> if there are more encapsulations in this stream; <code>false</code> otherwise.
	 *
	 * @throws MalformedStreamException if the stream ends unexpecetedly or fails to follow required syntax.
	 */
	public boolean readBoundary() throws MalformedStreamException {
		byte[] marker = new byte[2];
		boolean nextChunk = false;

		head += boundaryLength;
		try {
			marker[0] = readByte();
			marker[1] = readByte();
			if (arrayequals(marker, STREAM_TERMINATOR, 2)) {
				nextChunk = false;
			} else if (arrayequals(marker, FIELD_SEPARATOR, 2)) {
				nextChunk = true;
			} else {
				throw new MalformedStreamException("Unexpected characters follow a boundary");
			}
		} catch (IOException e) {
			throw new MalformedStreamException("Stream ended unexpectedly");
		}
		return nextChunk;
	}

	/**
	 * <p>Changes the boundary token used for partitioning the stream.</p>
	 *
	 * <p>This method allows single pass processing of nested multipart streams.</p>
	 *
	 * <p>The boundary token of the nested stream is <code>required</code> to be of the same length as the boundary token
	 * in parent stream.</p>
	 *
	 * <p>Restoring the parent stream boundary token after processing of a nested stream is left to the application.</p>
	 *
	 * @param boundary The boundary to be used for parsing of the nested stream.
	 *
	 * @throws IllegalBoundaryException if the <code>boundary</code> has a different length than the one being currently
	 *             parsed.
	 */
	public void setBoundary(byte[] boundary) throws IllegalBoundaryException {

		if (boundary.length != boundaryLength - BOUNDARY_PREFIX.length) {
			throw new IllegalBoundaryException("The length of a boundary token can not be changed");
		}

		System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
	}

	/**
	 * <p>Reads the <code>header-part</code> of the current <code>encapsulation</code>.</p>
	 *
	 * <p>Headers are returned verbatim to the input stream, including the trailing <code>CRLF</code> marker. Parsing is
	 * left to the application.</p>
	 *
	 * @return The <code>header-part</code> of the current encapsulation.
	 * @throws MalformedStreamException if the stream ends unexpecetedly.
	 */
	public String readHeaders() throws MalformedStreamException {
		int i = 0;
		byte b;
		// to support multi-byte characters
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		int size = 0;
		while (i < HEADER_SEPARATOR.length) {
			try {
				b = readByte();
			} catch (IOException e) {
				throw new MalformedStreamException("Stream ended unexpectedly");
			}
			if (++size > HEADER_PART_SIZE_MAX) {
				throw new MalformedStreamException("Header section has more than " + HEADER_PART_SIZE_MAX
						+ " bytes (maybe it is not properly terminated)");
			}
			if (b == HEADER_SEPARATOR[i]) {
				i++;
			} else {
				i = 0;
			}
			baos.write(b);
		}

		String headers = null;
		if (headerEncoding != null) {
			try {
				headers = baos.toString(headerEncoding);
			} catch (UnsupportedEncodingException e) {
				// fall back to platform default if specified encoding is not supported.
				headers = baos.toString();
			}
		} else {
			headers = baos.toString();
		}

		return headers;
	}

	/**
	 * <p>Reads <code>body-data</code> from the current <code>encapsulation</code> and writes its contents into the output
	 * <code>Stream</code>.</p>
	 *
	 * <p>Arbitrary large amounts of data can be processed by this method using a constant size buffer.</p>
	 *
	 * @param output The <code>Stream</code> to write data into. May be null, in which case this method is equivalent to
	 *            {@link #discardBodyData()}.
	 *
	 * @return the amount of data written.
	 *
	 * @throws MalformedStreamException if the stream ends unexpectedly.
	 * @throws IOException if an i/o error occurs.
	 */
	public int readBodyData(OutputStream output) throws MalformedStreamException, IOException {
		final InputStream istream = newInputStream();
		return (int) Streams.copy(istream, output, false);
	}

	/**
	 * Creates a new {@link ItemInputStream}.
	 *
	 * @return A new instance of {@link ItemInputStream}.
	 */
	protected ItemInputStream newInputStream() {
		return new ItemInputStream();
	}

	/**
	 * <p>Reads <code>body-data</code> from the current <code>encapsulation</code> and discards it.</p>
	 *
	 * <p>Use this method to skip encapsulations you don't need or don't understand.</p>
	 *
	 * @return The amount of data discarded.
	 * @throws MalformedStreamException if the stream ends unexpectedly.
	 * @throws IOException if an i/o error occurs.
	 */
	public int discardBodyData() throws MalformedStreamException, IOException {
		return readBodyData(null);
	}

	/**
	 * Finds the beginning of the first <code>encapsulation</code>.
	 *
	 * @return <code>true</code> if an <code>encapsulation</code> was found in the stream.
	 * @throws IOException if an i/o error occurs.
	 */
	public boolean skipPreamble() throws IOException {

		// first delimiter may be not preceded with a CRLF.
		System.arraycopy(boundary, 2, boundary, 0, boundary.length - 2);
		boundaryLength = boundary.length - 2;
		try {
			// discard all data up to the delimiter.
			discardBodyData();

			// read boundary - if succeded, the stream contains an encapsulation.
			return readBoundary();
		} catch (MalformedStreamException e) {
			return false;
		} finally {
			// restore delimiter.
			System.arraycopy(boundary, 0, boundary, 2, boundary.length - 2);
			boundaryLength = boundary.length;
			boundary[0] = CR;
			boundary[1] = LF;
		}
	}

	/**
	 * Compares <code>count</code> first bytes in the arrays <code>a</code> and <code>b</code>.
	 *
	 * @param a The first array to compare.
	 * @param b The second array to compare.
	 * @param count How many bytes should be compared.
	 *
	 * @return <code>true</code> if <code>count</code> first bytes in arrays <code>a</code> and <code>b</code> are
	 *         equal.
	 */
	public static boolean arrayequals(byte[] a, byte[] b, int count) {
		for (int i = 0; i < count; i++) {
			if (a[i] != b[i]) {
				return false;
			}
		}
		return true;
	}

	/**
	 * Searches for a byte of specified value in the <code>buffer</code>, starting at the specified
	 * <code>position</code>.
	 *
	 * @param value The value to find.
	 * @param pos The starting position for searching.
	 *
	 * @return The position of byte found, counting from beginning of the <code>buffer</code>, or <code>-1</code> if not
	 *         found.
	 */
	protected int findByte(byte value, int pos) {
		for (int i = pos; i < tail; i++) {
			if (buffer[i] == value) {
				return i;
			}
		}

		return -1;
	}

	/**
	 * Searches for the <code>boundary</code> in the <code>buffer</code> region delimited by <code>head</code> and
	 * <code>tail</code>.
	 *
	 * @return The position of the boundary found, counting from the beginning of the <code>buffer</code>, or
	 *         <code>-1</code> if not found.
	 */
	protected int findSeparator() {
		int first;
		int match = 0;
		int maxpos = tail - boundaryLength;
		for (first = head; (first <= maxpos) && (match != boundaryLength); first++) {
			first = findByte(boundary[0], first);
			if (first == -1 || (first > maxpos)) {
				return -1;
			}
			for (match = 1; match < boundaryLength; match++) {
				if (buffer[first + match] != boundary[match]) {
					break;
				}
			}
		}
		if (match == boundaryLength) {
			return first - 1;
		}
		return -1;
	}

	/**
	 * Thrown to indicate that the input stream fails to follow the required syntax.
	 */
	@SuppressWarnings("serial")
	public static class MalformedStreamException extends IOException {

		/**
		 * Constructs a <code>MalformedStreamException</code> with no detail message.
		 */
		public MalformedStreamException() {
			super();
		}

		/**
		 * Constructs an <code>MalformedStreamException</code> with the specified detail message.
		 *
		 * @param message The detail message.
		 */
		public MalformedStreamException(String message) {
			super(message);
		}
	}

	/**
	 * Thrown upon attempt of setting an invalid boundary token.
	 */
	@SuppressWarnings("serial")
	public static class IllegalBoundaryException extends IOException {

		/**
		 * Constructs an <code>IllegalBoundaryException</code> with no detail message.
		 */
		public IllegalBoundaryException() {
			super();
		}

		/**
		 * Constructs an <code>IllegalBoundaryException</code> with the specified detail message.
		 *
		 * @param message The detail message.
		 */
		public IllegalBoundaryException(String message) {
			super(message);
		}

	}

	/**
	 * An {@link InputStream} for reading an items contents.
	 */
	public class ItemInputStream extends InputStream implements Closeable {

		/* The number of bytes, which have been read so far */
		private long total;

		/* The number of bytes, which must be hold, because they might be a part of the boundary */
		private int pad;

		/* The current offset in the buffer */
		private int pos;

		/* Whether the stream is already closed. */
		private boolean closed;

		/**
		 * Creates a new instance.
		 */
		ItemInputStream() {
			findSeparator();
		}

		/**
		 * Called for finding the separator.
		 */
		private void findSeparator() {
			pos = MultipartReader.this.findSeparator();
			if (pos == -1) {
				if (tail - head > keepRegion) {
					pad = keepRegion;
				} else {
					pad = tail - head;
				}
			}
		}

		/**
		 * Returns the number of bytes, which have been read by the stream.
		 *
		 * @return Number of bytes, which have been read so far.
		 */
		public long getBytesRead() {
			return total;
		}

		/**
		 * Returns the number of bytes, which are currently available, without blocking.
		 *
		 * @return Number of bytes in the buffer.
		 * @throws IOException An I/O error occurs.
		 */
		public int available() throws IOException {
			if (pos == -1) {
				return tail - head - pad;
			}
			return pos - head;
		}

		/* Offset when converting negative bytes to integers */
		private static final int BYTE_POSITIVE_OFFSET = 256;

		/**
		 * Returns the next byte in the stream.
		 *
		 * @return The next byte in the stream, as a non-negative integer, or -1 for EOF.
		 * @throws IOException An I/O error occurred.
		 */
		public int read() throws IOException {
			if (closed) {
				throw new IOException("The stream is closed.");
			}
			if (available() == 0) {
				if (makeAvailable() == 0) {
					return -1;
				}
			}
			++total;
			int b = buffer[head++];
			if (b >= 0) {
				return b;
			}
			return b + BYTE_POSITIVE_OFFSET;
		}

		/**
		 * Reads bytes into the given buffer.
		 *
		 * @param b The destination buffer, where to write to.
		 * @param off Offset of the first byte in the buffer.
		 * @param len Maximum number of bytes to read.
		 *
		 * @return Number of bytes, which have been actually read, or -1 for EOF.
		 * @throws IOException An I/O error occurred.
		 */
		public int read(byte[] b, int off, int len) throws IOException {
			if (closed) {
				throw new IOException("The stream is closed.");
			}
			if (len == 0) {
				return 0;
			}
			int res = available();
			if (res == 0) {
				res = makeAvailable();
				if (res == 0) {
					return -1;
				}
			}
			res = Math.min(res, len);
			System.arraycopy(buffer, head, b, off, res);
			head += res;
			total += res;
			return res;
		}

		/**
		 * Closes the input stream.
		 *
		 * @throws IOException An I/O error occurred.
		 */
		public void close() throws IOException {
			close(false);
		}

		/**
		 * Closes the input stream.
		 *
		 * @param pCloseUnderlying Whether to close the underlying stream (hard close).
		 *
		 * @throws IOException An I/O error occurred.
		 */
		public void close(boolean pCloseUnderlying) throws IOException {
			if (closed) {
				return;
			}
			if (pCloseUnderlying) {
				closed = true;
				input.close();
			} else {
				for (;;) {
					int av = available();
					if (av == 0) {
						av = makeAvailable();
						if (av == 0) {
							break;
						}
					}
					skip(av);
				}
			}
			closed = true;
		}

		/**
		 * Skips the given number of bytes.
		 *
		 * @param bytes Number of bytes to skip.
		 *
		 * @return The number of bytes, which have actually been skipped.
		 * @throws IOException An I/O error occurred.
		 */
		public long skip(long bytes) throws IOException {
			if (closed) {
				throw new IOException("The stream is closed.");
			}
			int av = available();
			if (av == 0) {
				av = makeAvailable();
				if (av == 0) {
					return 0;
				}
			}
			long res = Math.min(av, bytes);
			head += res;
			return res;
		}

		/**
		 * Attempts to read more data.
		 *
		 * @return Number of available bytes
		 * @throws IOException An I/O error occurred.
		 */
		private int makeAvailable() throws IOException {
			if (pos != -1) {
				return 0;
			}

			// move the data to the beginning of the buffer
			total += tail - head - pad;
			System.arraycopy(buffer, tail - pad, buffer, 0, pad);

			// refill buffer with new data
			head = 0;
			tail = pad;

			for (;;) {
				int bytesRead = input.read(buffer, tail, bufSize - tail);
				if (bytesRead == -1) {
					// the last pad amount is left in the buffer
					// boundary can't be in there so signal an error condition.
					final String msg = "Stream ended unexpectedly";
					throw new MalformedStreamException(msg);
				}

				tail += bytesRead;

				findSeparator();
				int av = available();

				if (av > 0 || pos != -1) {
					return av;
				}
			}
		}

		/**
		 * Returns, whether the stream is closed.
		 *
		 * @return true, if the stream is closed, otherwise false.
		 */
		public boolean isClosed() {
			return closed;
		}
	}
}
